The general field of the invention is that of virus vaccines for protection of dogs against infection by canine parvovirus, their production and use. This invention is more particularly related to a subunit vaccine made by inserting canine parvovirus genes into a recombinant baculovirus expression vector. The vaccine is then produced by growing the resultant recombinant baculovirus in insect tissue culture or insects of a type which are a permissive host for the baculovirus replication and then harvesting the resulting vaccine material.
Parvovirus are characterized as small animal DNA viruses consisting of an isometric protein capsid and a short molecule of single-stranded DNA. Parvoviruses have been recovered and isolted from various animals over the years. Among them is the canine parvovirus which became an emerging disease of dogs in the world during a period beginning in 1978. At that time, the first canine parvovirus were isolated and vaccines were relatively rapidly developed to combat this disease which is characterized in dogs by diarrhea, fever, and leukopenia (relative lymphopenia). Starting in 1978, over the space of 3 years, 3 different kinds of canine parvovirus vaccines were developed to combat a wide spread outbreak of the then apparently new viral disease. They are reported as three landmark inventions by Professors in the Vaterinary Colleges of Cornell University, James A. Baker Institute for Animal Health. They are as follows:
(1) U.S. Pat. No. 4,193,991, issued Mar. 18, 1980 to Max J. G. Appel and Leland E. Carmichael which relates to an inactivated (killed) canine parvovirus vaccine.
(2) U.S. Pat. No. 4,193,990, issued on Mar. 18, 1980 to Max J. G., Appel, Leland E. Carmichael and Fredric W. Scott which relates to this use of the modified live or chemically activated feline panleukopenia virus as a canine parvovirus vaccine.
(3) U.S. Pat. No. 4,303,645, issued Dec. 1, 1981 to Leland E. Carmichael, Max J. G. Appel, and Douglas D. McGregor which relates to the use of the modified (attentuated) live canine parvovirus as a canine parvovirus vaccine.
These vaccines have functioned very well in the field over the years and have stemmed the outbreak of canine parvovirus all over the world. For the most part, this disease is well controlled following the proper vaccination program. However, the inactivated vaccines identified hereinabove tend to provide protection for a relatively short time and the modified live canine parvovirus vaccine is considered by some to have the potential for becoming virulent.
Over the years the canine parvovirus known as type-2 (CPV) has been studied by many and the DNA sequence of the same is reported in a scientific article entitled Parvovirus genome; Nucleotide sequence of H-1 and mapping of its genes by hybrid-arrested translation by Rhode et al. appearing in the Journal of Virology volume 54, pages 630-633. In addition Parrish et al. have studied the antigenic structure of canine parvovirus type-2 and have reported their work in a scientific article entitled Antigenic Structure and Variation of Canine Parvovirus Type-2 Feline Panleukopenia Virus, and Mink Enteritis Virus, in Virology volume 129 pages 401-414. This article identifies three protein categories relating to canine parvovirus antigenic reactivity, However, following the choice of many scientists for the purpose of describing the present invention, the description herein identifies only one of these categories which is viral protein VP-2 because it is the major immunogenic parvovirus capsid. Infection by canine parvovirus may be prevented by vaccinating animals with either live attenuated or inactivated virus vaccines. Antibody level is the prime mediator of protection. Several vaccines containing inactivated canine parvovirus have been marketed, but because of the small amounts of antigen present these generate low levels of short-lived immunity.
To produce more antigen than can be obtained from virus-infected cell cultures, several groups have attempted to develop vaccines by expressing portions of the CPV PV-2 gene in E. coli (see Carlson et al. 1984, Expression of feline panleukopenia virus antigens in E. coli. In Modern approaches to vaccines Cold Spring Harbor, N.Y. pages 195-201). Although these produce some VP-2 peptides, none has been shown to immunize animals efficiently or to express the intact antigenic sites of the protein responsible for neutralization. It appears that the VP-2 protein cannot be produced in E. coli expression systems in a form which will efficiently immunize animals and there is not a good vaccine to control canine parvovirus which is of significant veterinary importance.
A development relating to the use of baculovirus expression vectors to express foreign genes by recombinant baculoviruses offered a possibility to solve this important problem through further laboratory discovery. The prior art, with respect to baculovirus as it relates to the present invention is summarized in two scientific articles. They are:
1. "Production of Human Beta Interferon in Insect Cells Infected with a Baculovirus Express Vector", by Smith et al. appearing in Molecular and Cellular Biology, December 1983, volume 3, pages 2156 and 2165, and
2. "Trends in the Development of Baculovirus Expression Vectors", by Luckow et al. appearing in Bio/Technology, January 1988, volume 6, pages 47-55.
The baculovirus vector has in other circumstances utilized the highly expressed and regulated Autographa californica nuclear polyhedrosis virus (AcMNPV) polyhedrin gene promoter and open reading frame modified for the insertion of foreign genes. Use of such a vector allows for the insertion of eukaryotic genes into the baculoviruses.